Issue 62

N.E. Tenaglia et alii, Frattura ed Integrità Strutturale, 62 (2022) 212-224; DOI: 10.3221/IGF-ESIS.62.15

introduce changes in the steel’s macrostructure compared to Steel B (0.12% of Ti). The same behavior was found for Heavy KB, as can be observed in Fig. 13 and Tab. 3. This can be explained because despite the addition of 0.12% of Ti promotes a fine dispersion of Ti(N,C) particles, when the Ti concentration rises to 0.2%, the size of Ti(N,C) particles increases in size while its amount could decrease, losing your refiner effect. So, for the steel under study, the refining effect would be achieved for titanium concentrations higher than 0.1% (point P in Fig. 1). Similar results were reported by Ohno et. al. [11] for a 0.2%C cast steel.

Sample

%Ti

FTF zones size [mm]

Grain size[mm]

<0.01

0.39 0.27 0.25 0.94 0.66 0.67

1.84 1.14

1-inch KB

0.12

0.2

- - - -

<0.01

Heavy KB

0.12

0.2

Table 3: Effect of Ti additions on grain and FTF zones size.

Mechanical properties: Hardness The results of hardness measurements as a function of Ti content and cast part size are plotted in Fig. 14. The variation of hardness values can be explained by means of the competition of three phenomena: proeutectoid ferrite/pearlite ratio, phases size and the presence of hard Ti precipitates. In general, for the samples under study, the hardness increases as Ti content is higher. In the case of 1-inch KB, the highest hardness value of 232 HV corresponds to a Ti content of 0.12%. Despite having a large amount of proeutectoid ferrite, which would cause a decrease in the hardness value, the samples corresponding to 1-inch KB - Steel B showed a finer microstructure and the presence of dispersed Ti(N,C) hard particles, which cause an increase of the hardness. In the case of 1-inch KB with 0.2% of Ti, the large amount of proeutectoid ferrite and a similar density of Ti(N,C) particles promote lower hardness, compared to samples with 0.12% of Ti. Regarding to Heavy KB, the addition of Ti caused an increase of the hardness values from 179 HV to 228 HV, which could be explain for both, the finer microstructures and the presence of Ti(N,C) particles. The hardness values for Steel B and C were similar (226HV and 228 HV respectively).

Figure 14: Hardness values as a function of cast part size and Ti content.

Mechanical properties: Tensile properties The effect of Ti content and cast part size on tensile properties is plotted in Fig.15. In the case of 1-inch KB, the tensile strength was slightly modified with Ti additions. In agreement with the hardness, the highest value was obtained for the

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